This invention relates to hingeless composite rotor hubs for rotary wing aircraft, and more particularly to strap member configurations for connecting rotor blades to a central rotor hub in such systems.
Many of the basic design limitations of rotor and blade assemblies in rotary wing aircraft are reasonably well known. Thus, although the interaction of the various parameters is quite complex, the various loading, stress, bending, and the like factors, and their interaction with one another generally, are reasonably well formulated. Designers have considerable latitude to trade off these factors against one another, but certain basic performance factors stand as ultimate design goals, and the various components of the rotor system must in all events meet datum performance criteria.
One critical component in rotor systems or rotary wing aircraft is the central hub portion to which the rotor blades are attached. Basic operational constraints of rotary wing flight impose substantial functional complexity upon the hub, necessitated by various needs to control accurately multi-directional displacement of the blades, and to vary the pitch thereof. Variations in displacement, pitch, and stress upon the blades must be provided at different locations of the rotation cycle, in order to provide compensation for the well known loads, stresses, and aerodynamic factors to which the rotating blades are subjected. Further, the hub element must fulfill these various functions whether the aircraft is at rest, hovering, experiencing translational motion, or the like. Earlier designs involve complex articulated (i.e., multiple hinged) hubs and blades, but more recently hingeless systems have been developed which are intended to meet the various functional constraints generally involved with rotor hub systems, and furthermore to improve such base line parameters as structural simplicity, maintenance ease, low cost, and the like.
It is accordingly a primary object of the present invention to provide a composite hingeless rotor hub system which satisfies the various functional and structural limitations to which all rotor systems are subjected, and further which is reliable and relatively simple structurally, and advantageous from the standpoint of maintenance simplicity and cost.
It is a further object to provide such a hingeless rotor hub system wherein the simplicity of design also involves weight reduction, minimal manufacturing costs, and improved ease of installation.
In accordance with yet another object of the present invention, adaptability to folding rotor blade configurations and to either main or tail rotor configurations is highly desirable.
More particular functional objects of the present invention relate to the elimination altogether of heaving, or flap deflection caused by pitch control inputs, coupled with reduction of control loads, without imposition upon the necessary pitch variation capability.
Since hingeless rotor systems involve rigid attachment of the hub to the blades, it is another object of the present invention to provide a composite hingeless rotor hub possessing relatively low blade loads.